The present invention relates to the field of electronic thermometers, and more specifically relates to an electronic thermometer which is capable of providing a wide range of temperature measurement and yet can provide high resolution temperature measurement within a desired temperature range.
In a conventional type of electronic thermometer, such as for example an electronic clinical thermometer, the oscillation frequencies of an oscillator unit which has a reference resistor and a temperature sensitive resistor are compared by a comparison means which switches over between the reference resistor and the temperature sensitive resistor for each sampling time, and the digital data outputted from the comparison means are inputted into a temperature data conversion means which may include a ROM or the like, and which converts these digital data for display on a display unit.
According to one particular such prior art type of electronic clinical thermometer, the measuring range is set to (as an example) 35 deg C. to 42 deg C. If the value of the measured temperature is less than the low point of this measuring range, i.e. is less than 35 deg C., then no specific indication of temperature is shown on the display unit, but only a letter "L" is displayed thereon, indicating low temperature. And similarly, if the value of the measured temperature is greater than the high point of the measuring range, i.e. is greater than 42 deg C., then again no specific indication of temperature is shown on the display unit, but only a letter "H" is displayed thereon, indicating high temperature. If the value of the measured temperature is within the measuring range, i.e. is greater than 35 deg C. and is less than 42 deg C., then a specific numerical indication of temperature is shown on the display unit, typically at a resolution of the order of 0.01 deg C. This is done in order to secure the necessary resolution power within the range of temperature which it is important to sense accurately, while maintaining the compactness and cheapness of the temperature data conversion means and of the thermometer as a whole, by reducing the amount of data needed to be stored by said temperature data conversion means.
However, a problem arises with such an electronic clinical thermometer in that the response time between the start of measurement and the appearance of a temperature reading on the display tends to be long. In other words the time interval during which the letter "L" only is visible on the display tends to be long, and the user sometimes becomes irritated with this. Further, sometimes is is desired to use the electronic clinical thermometer for another use than clinical work, i.e. for measuring temperatures which lie outside the normal range of temperature for a clinical thermometer which naturally is centered approximately around human body temperature. If in such circumstances the range of temperature measurement is expanded to, for example, -5 deg C. to 79 deg C., then, if the resolution power of the thermometer is maintained as being of the order of 0.01 deg C. which is that typically used for clinical purposes, the problem arises that the capacity of the memory of the temperature data conversion means is strained and may be exceeded. Further, if said temperature data conversion means is in any case made large enough to hold all the required data, then further problems arise in that the counter included in the comparison means is required to have a forbiddingly great number of bits, and the sampling time required for AD conversion tends to become long. Therefore, it has been difficult in the prior art to expand the range of temperature measurement available from an electronic thermometer, while maintaining the accuracy of temperature measurement, i.e. the temperature resolution, provided thereby.